linux-kernel - Re: [BISECTED] "conservative" cpufreq governor broken

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 7 Oct 2009 12:42:15 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Eero Nurkkala <ext-eero.nurkkala@...ia.com>
cc:	ext Steven Noonan <steven@...inklabs.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Greg KH <greg@...ah.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [BISECTED] "conservative" cpufreq governor broken

On Wed, 7 Oct 2009, Eero Nurkkala wrote:
> For some reason, this path is taken: 
> if (ts->nohz_mode == NOHZ_MODE_INACTIVE)
>         goto end;

Well, probably because the machine never switched to NOHZ :)
 
> > Also, this fix should probably be passed on to Greg K. H. (so it goes
> > in 2.6.31-stable) as well as Ingo Molnar (so it goes into -tip, and
> > hopefully to Linus for 2.6.32). Both CC'd.

Don't worry, it'll go the right way. No need to cc the world and some
more :)
 
> > - Steven
> 
> From: Eero Nurkkala <ext-eero.nurkkala@...ia.com>
> Date: Wed, 7 Oct 2009 11:54:26 +0300
> Subject: [PATCH] NOHZ: update idle state properly
> 
> Commit f2e21c9610991e95621a81407cdbab881226419b
> had unfortunate side effects with cpufreq governors on
> some systems.
> 
> If NOHZ_MODE_INACTIVE was set, ts->inidle was not being
> set. Then, all subsequent calls from irq_exit() bypassed
> calls to tick_nohz_start_idle() which resulted in wrong
> information passed to cpufreq governors. Fix this by
> updating the state of ts->inidle where it fits the best.

Hmm, nasty that code silently relies on NOHZ functionality even when
NOHZ is not active. That needs a big fat comment at least.

Nice detective work though !

Thanks,

	tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/